I understand the work around to 'complete' my database with all missing month and that works perfectly and easily with the example I enclosed.

Unfortunately, I might have over simplified the example compared to my real data. Indeed, my data is a bit more complex in the sense that I have many more dimensions. To continue with the same example, let' say that my database includes further dimensions such as Market, Region, Key Account, Products. And I want the users to be able to filter on any of these dimensions and see the monthly data including the months without data. I have enclosed the updated workbook, but please consider that this is still a simplified version of the reality as I have thousands of products.

In order to use your workaround (if am I not wrong) I would have to create a calendar file that includes all possible combinations of Market, Region, Key Account, Products and Months to ensure that I capture all possible options. Plus, I would have to maintain that database for every new Product or change in Key Account.

Again I recon that your solution can work, but I am afraid it is not manageable with my real data.

You don't have to create the combination of dimension with calendar in this case. I did the same join with your new workbook and below is the result by play around some of the dimension filter as well.

Anyway, I have replicated in the enclosed workbook what I think is a limitation of your proposal:

In this example I have sales covering all days of February on various products with exception of product BB. The joint with Calendar will not create a line for Feb for BB and therefore a filter on product BB (and Null) will show all months but February.

Please let me know if I am missing something?

One additional downside of your proposal is that the user always has to filter on his selection + 'Null' which is not very intuitive.